Johnson set to demand an extra £5 billion a year for NHS in Cabinet meeting today.

The foreign secretary believes that the Conservatives must do for the NHS to take on the growing threat of Jeremy Corbyn's Labour.

May is under pressure from restless Conservative MPs to be more ambitious.

LONDON — Philip Hammond has slapped down his government colleague Boris Johnson's demand that the NHS be given an extra £5 billion a year after Britain leaves the European Union.

Johnson is reportedly set to challenge Prime Minister Theresa May to give an additional £100 a week to the NHS after Brexit in a meeting of Cabinet on Tuesday morning.

The foreign secretary will urge May to devote more money to the under-pressure health service and will not relent until the prime minister agrees to the policy, The Times reports.

However, speaking in Brussels where is meeting European finance ministers today, Hammond rebuked Johnson's demand and reminded him of his role in government.

"Mr Johnson is the foreign secretary," a defiant Hammond said.

"I gave the health secretary an extra £6bn at the recent budget and we will look at departmental allocations again at the spending review when that takes place."

Johnson reportedly believes that the Conservatives must do more to help the NHS to convince the public that it is serious about protecting the health service and fight off the threat of Jeremy Corbyn's Labour Party.

Official figures showed that over 17,000 people waited in the back of an ambulance for more than hour as they waited for treatment over Christmas, while 91.7% of hospital beds in Britain were full.

"Boris believes that if the Tories are going to beat Corbyn at the next election they must make the NHS a top priority and deliver new funding," an ally of Johnson told The Times.

"Every poll conducted shows the NHS is top of swing-voter concerns and every expert says it needs more money. The cabinet will have to act and the sooner the better."

They insisted that his demand for money has nothing to do with the Brexit campaign's contentious claim that leaving the European Union will give Britain an extra £350 million a week to give to the NHS.

"This isn't about the referendum — it's about delivering on the No 1 concern for the public and beating Corbyn."

Johnson is expected to make the case for more money for the NHS when Health Secretary Jeremy Hunt updates his Cabinet colleagues on how the service is coping with the winter crisis.

The foreign secretary's intervention will not be the first time he has challenged the prime minister on policy.

Johnson was at the eye of a media storm last year when he penned a 4,000 article for The Daily Telegraph outlining his personal vision for Brexit just days before May's highly-anticipated Florence speech.

He is also set to challenge the prime minister at a time when she is under pressure from the MPs on the Tory backbenchers to be bolder in her approach to policy.

Conservative MPs Sarah Wollaston, Heidi Allen and Nick Boles last week expressed their "disappointment" in May for not agreeing to a cross-party demand to take greater action to protect the future the NHS and social care.

Boles tweeted:

In November 90 MPs, including 33 Tories, signed a letter to the prime minister suggesting an NHS and Social Care Convention be created to help establish a "sustainable" model for healthcare.